Borated lubricating oil additives of many types have been proposed for use in lubricating oils. Principal among these are borated nitrogen-containing polymer lubricating oil additives such as dispersants, which are typically prepared by reacting a polymeric nitrogen-containing dispersant with a boronating agent, such as boric acid. Conventional borated dispersants include borated polyisobutenyl succinimides and borated Mannich base dispersants which are themselves prepared by borating a Mannich base reaction product derived from polyalkyl-substituted phenols, aldehyde and polyamine.
For example, when the nitrogen-containing dispersant comprises polyisobutenyl succinimide, it can be reacted with boric acid; water is evolved and the resulting salt product is the borated polyalkene succinimide. However, the above reactions also yield undesirable by-products, which are oil insoluble species which are generally required to be removed from the borated lubricating oil additive before it is either sold or incorporated into either fully formulated lubricating oils or into concentrates (so-called "adpacks" which are concentrates containing a variety of selected components). These oil insoluble species are detectable by adding solvent (normally at a 50 volume % level) to the product and spinning the dilute product in a centrifuge tube. These insoluble species are generally measured as a volume percent of the total graduated centrifuge tube.
U.S. Pat. No. 3,087,936 is directed to the preparation of a reaction product of an aliphatic olefin polymer succinic acid or anhydride with an amine, followed by reacting the resulting product with a boron compound, such as boric acid.
U.S. Pat. No. 3,313,727 is directed to the preparation of stable dispersions of alkali metal borates in lubricating oil wherein a hydrated alkali metal borate is admixed with an emulsifying agent in an amount sufficient to maintain the borate particles as stable dispersion. The particles are said to be almost entirely less than 1 micron in size and, for the most part, less than 0.5 microns. Suitable alkali metal borates are metaborates and tetraborates of sodium and potassium having from 1 to 4 waters of hydration. Neutral dispersants such as alkenyl succinimides of alkaline amines can also be present in these compositions.
U.S. Pat. No. 4,025,445 relates to boron amide lubricating oil additives which are obtained by mixing a chlorinated hydrocarbon with an alkylene polyamine to form a nitrogen-containing reaction product which is then combined with a boron compound for reaction of the boron compound with the nitrogen-containing reaction product. The additive thus formed is disclosed to be effective as an antirust crankcase lubricating oil additive. The boron compounds which were said to be useful include boron oxide, boron trifluoride, boron tribromide, boron trichloride and boric acid. Examples in this patent illustrate the use of an unspecified powdered anhydric boric acid, and filtering of the resulting boric reaction product.
U.S. Pat. No. 4,419,387 is directed to preparation of a boric acid having improved handling properties. The patentee discloses that in the manufacture of boric acid, crystals of fine particle size (less than about 75 microns in size) are generally separated from the product, since these fines are unsuitable for most customers due to their dustiness and difficult handling properties. The patentee contacts boric acid particles with gaseous ammonia to reduce the lubricity of the boric acid crystals. Use of such reduced lubricity boric acid crystals in glass manufacture is disclosed. U.S. Pat. No. 4,487,803 contains a similar disclosure.
U.S. Pat. No. 4,578,086 is directed to a method for controlling boric acid particle size distributions for boric acid crystallized from saturated aqueous feed solutions thereof. It is disclosed that crystals in boric acid prepared from prior art processes generally are of a mean particle size of about 190 to about 195 microns or less, and that this mole size causes problems with subsequent purification, handling and storage. The patentee employs a water soluble acrylamide homopolymer or copolymer in the aqueous solution from which the boric acid is crystallized in order to increase the mean particle size of the crystal and boric acid.
U.S. Pat. No. 4,801,404 is related to boric acid suspensions useful for biocide components and wood preservatives and as fire retardant components for wood treatments, which comprise concentrated, finely dispersed suspensions of boric acid and a small amount of soluble borate salt in an aqueous medium. The patentee contrasts the patent's suspension with prior art highly concentrated to solutions of boric acid and water soluble amines or polyamines, and points out that the amine components interfere in many uses in that this component is additionally introduced into the resulting mixtures to which the concentrated boric acid solution is applied.
U.S. Pat. No. 4,834,913 relates to an apparatus and method for forming finely divided dry boric acid.